Method and a device for milking an animal

ABSTRACT

The invention relates to a method and a device for milking an animal, which includes at least a pair of teatcups ( 2 ). A pulsator ( 12 ) is arranged, via a pulsation chamber ( 4 ) of each teatcup ( 2 ), to subject its liners ( 3 ) for a cyclically pulsating pressure from the outside, which pressure has a cycle with a time period T. The cycle includes a first opening phase (a), a second open phase (b), a third closing phase (c) and a fourth closed phase (d). When both the time periods of the second open phase (b) and the fourth closed phase (d) are less than the half time period for the total cycle, T the cyclically pulsating pressures of the respective pulsation chambers are controlled by a control ( 15 ) in such a way that a flow of milk between the two teatcups of the respective pair is prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and a device for milking an animal, bythe use a milking machine, which comprises at least one pair of teatcupswhich each comprising a liner for receiving a teat of the animal,wherein these liners internally are subjected to a subpressure forextracting milk from the respective teats, and which comprises apulsator arranged, via a pulsation chamber of each teatcup, to subjectthe liners of the teatcup to a cyclically pulsating pressure from theoutside, which pressure has a cycle with a time period T, wherein saidcycle comprises

a first opening phase a, which has a first time period t₃ and duringwhich the pressure in the pulsation chamber drops from a first pressurelevel to a second pressure level,

a second open phase b, which has a second time period t_(b) and duringwhich the pressure in the pulsation chamber is essentially constant atthe second pressure level,

a third closing phase c, which has a third time period t_(c) and duringwhich the pressure in the pulsation chamber rises from the secondpressure level to the first pressure level,

a fourth closed phase d, which has a fourth time period t_(d) and duringwhich the pressure in the pulsation chamber is essentially constant atthe first pressure level.

2. Description of the Prior Art

Such methods and devices are previously well known and are used byconventional milking machines. A conventional milking procedure maycomprise an initial milking period I, during which the milk flow starts,which period is arranged to stimulate and massage the teat for thepurpose of starting the Milk flow. Thereafter, a main milking period IIfollows and finally a terminating milking period Ill. The initialmilking period may according to known technique be performed with afaster pulsation than the main milking period in order to increase thestimulating effect, The most common type of pulsator used has a ratio,i.e. a proportion between an open and a closed position from 70:30 to60:40. Usually, such a pulsator has two outlets, which give a cyclicallypulsating pressure to a pair of teatcups. The cyclically pulsatingpressure is phase displaced 180° between these two teatcups, so that anopen phase of one of the teatcups essentially occur at the same time asa closed phase of the other teatcup. In such a way it is possible todecrease the fluctuation of the vacuum level of the milking member anduse the capacity of the existing milking equipment at maximum. However,since at a stimulating initial milking period has a faster pulsation,the time periods of the open and closed phases decrease while theopening and closing phases have an essentially constant time period,which first of all is determined by the properties of the liner and theair volumes at the pulsation side. Therefore, the opening and closingphases take up a relatively greater part of the time period of the totalcycle. It is optimal with a ratio of 50:50 for an open/closed proportionduring such an increased pulsation speed. It depends on the fact that,the closed phase will, during the faster pulsation at for example aratio of 70:30, be very short and possibly not even occur.

A problem, which arises at a ratio of 50:50 and with a phasedisplacement of 180°, is that an opening phase and a closing phase occurat the same time for a pair of teatcups. This results in a pressuredifference and thus an air flow arising between the internal spaces ofthe two liners, wherein milk in form of droplets may be sucked from oneteat via the milk claw and up through the short milk tube leading to theother teatcup and into its liner and there hit the other teats This flowof milk from one teatcup to another is called “cross-flow” and may occurat a very high speed. The droplets may contain bacteria, which maypenetrate into the teat canal of the teat and thereby cause infections.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method and a devicewhich make it possible to avoid the occurrence of a flow of milk betweentwo teatcups, so-called cross-flow, especially in connection with a fastpulsation of a pulsator and with a ratio of about 50:50.

This object is achieved according to the invention by controlling, whenboth the second T_(b) and fourth T_(d) time periods are less than thehalf time period T for the total cycle, the cyclically pulsatingpressures of the respective pulsation chambers in such a way that a flowbetween the two teatcups of the respective pair is prevented. Thiscontrol may be performed in several ways, i.e. by a variation of thephase displacement between the two cycles or by a suitable variation ofthe pulsation speed for the two cycles.

According to a preferred embodiment of the invention, the cyclicallypulsating pressures of the respective pulsation chambers are controlledin such a way that the first opening phase of one of the teatcups doesnot occur at the same time as the third closing phase of the otherteatcup. Above all, when these phases coincides, the risk for said flowor milk between the two teatcups occurs. The most practical is that theincluding cycles have an essentially equal time period with respect tothe included phases. Thereby, the cyclically pulsating pressures of therespective pulsation chamber may be controlled so that they have a phasedisplacement which prevents an opening and closing phase from occurringat the same time, wherein the phase displacement is so controlled thatit does not exceed a maximum phase displacement F_(max), wherein

F_(max)=(t_(d)/T)*360° if t_(d)<t_(b), and

F_(max)=(t_(b)/T)*360° if t_(b)<t_(d).

These conditions may in an easy manner be derived mathematically, withthe condition that said cycles have identical time periods, which onlyare phase displaced. Advantageously, the cyclically pulsating pressuresof the respective pulsation chambers are controlled to be so close tosaid maximum phase displacement as possible, wherein said phasedisplacement is controlled to be at least greater than F_(max−)20°.

According to another advantageous embodiment of the invention, thepulsation frequency is controlled to be equal to or less than 200 cyclesper minute. Thereby, the cyclically pulsating pressures of therespective pulsation chambers may be controlled to have a constant phasedisplacement in the interval 80°-100°. In this case, a phasedisplacement of 90° may be suitable. Thereby, no risk of said flowbetween the two teatcups arising occurs as long as the pulsationfrequency is less than 200 cycles per minute. If the pulsation frequencyis controlled to be between 200-400 cycles per minute, a constant phasedisplacement ought to be controlled to be in the interval 35°-55°,preferably the phase displacement 45° may be selected

According to a preferred embodiment of the invention, the method isarranged to be performed when the first pressure level is an atmosphericpressure and when the second pressure level is a subpressure of about 50kPa, i.e. normal pressure levels for milking machines.

According to another advantageous embodiment of the invention, themethod is arranged to be performed during the initial massage period Iwhich occurs before the main milking period II.

The invention is also related to a device for performing the methodabove. The device comprises control means, which are arranged to controlthe cyclically pulsating pressures according to the above-mentionedmethod. Thereby, the control means may comprise a control unit which byknowledge of the pulsation speed of the included cycles, i.e. timeperiod and other features, influences the pulsator so that an openingphase does not occur at the same time as a closing phase of a pair ofthe teatcups. The control unit may be a calculating unit, which controlsthe cyclically pulsating pressure of the respective pulsation chambersso that they have a phase displacement which does not exceed a maximallycalculated phase displacement F_(max). The control unit may also bedesigned in a more simple manner so that it controls the cyclicallypulsating pressures of the respective pulsation chambers to have aconstant phase displacement within a pulsation frequency range. Thisconstant phase displacement may be 90° at a pulsation frequency under200 cycles per minute and 45° at a pulsation frequency between 200-400cycles per minute.

Furthermore, said control means may be provided to perform said controlduring an initial massage period I which occurs before the main milkingperiod II.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is described by way of examples withreference to the attached drawings, in which

FIG. 1 shows a milking machine with a control unit according to theinvention,

FIG. 2 shows how a flow of milk between two teatcups, so-calledcross-flow, may occur,

FIG. 3 shows a cycle with a pulsation pressure comprising four phases,

FIG. 4 shows two cycles with a phase displacement of 180° and a ratio ofabout 70:30,

FIG. 5 shows two cycles with a phase displacement of 180° and a ratio of50:50, and

FIG. 6 shows two cycles with a phase displacement of 90° and a ratio of50:50.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a milking machine 1 with a pair of teatcups 2. It is to benoted that only one pair of teatcups is shown but the milking machine 1may comprise several pairs of teatcups. Each teatcup 2 comprises a liner3 for receiving a teat of an animal. The external surface of the liner 3forms a pulsation chamber 4 with the internal surface of the teatcup 2.Each liner 3 comprises internally a milk guiding passage, which viashort milk tubes 6 leads the milk to a milking claw 7. Thereafter, themilk is transported through a long milk tube 8 to a main milk pipeline9. Short pulse tubes 10 connect the pulsation chambers 4 of the teatcups2, via the milking claw 7 and long pulsation pipelines 11, to a pulsator12. The pulsator 12 is arranged to alternatively reduce the pressure inthe pulsation chambers 4 of a pair of teatcups. An adjustment device 13,which is arranged to adjust the pressure in the pulsator 12, isconnected to a vacuum pipeline 14. According to the invention, a controlunit 15 is provided to control the pulsator 12 so that a flow of milkbetween the two teatcups 2 is prevented.

From FIG. 2 it is evident how said flow between the two teatcups 2 in apair may occur. By the fact that the pulsator 12 transfers a cyclicallypulsating pressure to the respective pulsation chamber 4 of each teatcup2, respective the liner 3 will perform an opening A and closing C motionwhen the pressure is changed in the pulsation chamber 4 between a firstP1 and a second P2 pressure level. The liners 3 are internally, via themilk tube 6 and the milking claw 7, subjected to a subpressure, whichusually is designated as a vacuum. The greatest risk of said flow ofmilk between the two teatcups 2 occurs when the liner 3 of one of theteatcups performs an opening motion A at the same time as the liner 3 ofthe other teatcup 2 performs a closing motion C. In FIG. 2, the liner 3of the left teatcup 2 performs an opening motion A while the liner 3 ofthe right teatcup 2 performs a closing motion C. Thereby, the liner 3which performs an opening motion A will expand its inner volume, whereina temporary subpressure in relation to the pressure in the milking claw7 is obtained. In a corresponding way, the liner 3 which performs aclosing motion C will reduce its inner volume, wherein a temporaryoverpressure is obtained in this liner 3 in relation to the pressure inthe milking claw 7. By this temporary pressure difference in therespective liners 3 an air stream may move from the liner 3 having thetemporary overpressure to the liner 3 having the temporary subpressure.This air stream is marked with arrows 16 in FIG. 2. Thereby a riskoccurs that milk, essentially in form of droplets 17, is sucked by theair stream. Such droplets 17 may obtain a very high speed, up to 12 m/s.Thereby, the milk droplets 17 may penetrate into the teat canals andresult in infections of these if the milk contains bacteria. Thereby, aninfected teat may easily infect another teat of the same animal.

FIG. 3 shows a cycle of the cyclically pulsating pressure in thepulsation chamber 4. In the pulsation chamber 4 prevails initially afirst pressure level P1 which usually is an essentially atmosphericpressure. During a first opening phase a, the pressure in the pulsationchamber 4 drops to a second pressure level P2, which may be asubpressure of the size of 50 kPa. This first phase a has a time periodt_(a). Thereafter, a second open phase b is initiated during which thepressure in the pulsation chamber 4 is essentially constant at thesecond pressure level P2 During this phase milk is extracted out of theteat. This phase b has a second time period t_(b), Then a third closingphase c is initiated, during which the pressure in the pulsation chamber4 rises from the second pressure level P2 to the first pressure levelP1. The third phase c has a third time period t_(c). Finally, the cyclehas a fourth phase d, during which the pressure in the pulsation chamberis essentially constant at the first pressure level P1. The fourthclosed phase d has a fourth time period t_(d). The cycle has a totaltime period T which is the sum of the included time periods of thephases. The time period T is determined by the pulsation frequency ofthe pulsator 12.

FIG. 4 shows how the cyclically pulsating pressure varies with the timefor a pair of teatcups 2 by conventional milking during the main milkingperiod I. The ratio between an open, and closed position of the liners 3are in this case about 70:30. This ratio is calculated as the proportionbetween the opening phase a and the open phase b in proportion to theclosing phase c and the closed phase d By a conventional milking method,said cycles are displaced 180° and have a pulsation frequency of about60 cycles/min. The open phase b dominates here and by the fact that thecycles are displaced 180° any of the cycles of the pairs of teatcupswill always have the phase b, i.e. the opening phase a and the closingphase c will by that reason never occur at the same time. As long as thetime period t_(b) for the open phase b is greater than the half timeperiod T for the total cycle any of the cycles of the pair of teatcupswill always have the phase b at the displacement of 180°. Thecorresponding argumentation is valid also for the closed phase d if itwould have a greater time period than the open phase b. Usually, problemonly arises when one wants to have a ratio about 50:50 or increase thepulsation frequency considerably because the time periods of the bothphases b and d may then be less than the half time period d of the totalcycle. FIG. 5 shows such an example with a ratio of 50:50. Such a ratiomay be desirable during an initiating massage period I which occurbefore the main milking period II. In that case, it is not possible tokeep a phase displacement of 180° between the cycles since an openingphase a of one of the cycles. will occur at the same time as a closingphase c of the other cycle. If the two cycles are identical with respectto the time periods of the included phases one may, for avoiding that anopening phase a and a closing phase c occur at the same time, derive arelationship with a maximum phase displacement F_(max) between thecycles which is not to be exceeded, wherein F_(max) is equal with

F_(max)=(t_(d)/T)*360° if t_(d)<t_(b), and

F_(max)=(t_(b)/T)*360° if t_(b)<t_(d).

Thereby, the control unit 15 may be provided to control the phasedisplacement of the cycles so that this maximal phase displacementF_(max) is not exceeded. This control may be calculating so that thephase displacement varies in response to the values of the includedcycles, according to the formula above, or be constant within determinedpulsation frequency ranges. FIG. 6 shows the cycles in FIG. 5 but with aphase displacement of 90°. As is visible, no opening phase a occurs hereat the same time as a closing phase c of the respective cycles.

Certainly, the invention is not restricted to the described embodimentsin the figures, but may be varied freely within the scope of the claims.

What is claimed is:
 1. A method for milking an animal, by using amilking a machine, which comprises at least one pair of teatcups eachcomprising a liner for receiving a teat of the animal, wherein theseliners internally are subjected to a subpressure for extracting milkfrom the respective teats and which comprises a pulsator arranged, via apulsation chamber of each teatcup, to subject the liner of the teatcupto a cyclically pulsating pressure from the outside, including the stepof subjecting the liner to a cycle of pulsating pressure with a timeperiod T, wherein said cycle comprises: a first opening phase, which hasa first time period t_(a) and during which the pressure in the pulsationchamber drops from a first pressure level to a second pressure level; asecond open phase, which has a second time period t_(b) and during whichthe pressure in the pulsation chamber is substantially constant at thesecond pressure level; a third closing phase, which has a third timeperiod t_(c) and during which the pressure in the pulsation chamberrises from the second pressure level to the first pressure level; and afourth closed phase, which has a fourth time period t_(d) and duringwhich the pressure in the pulsation chamber is substantially constant atthe first pressure level, wherein when both the second t_(b) and fourtht_(d) time periods are less than the half time period T for the totalcycle, the cyclically pulsating pressures of the respective pulsationchambers are controlled in such a way that a flow of milk is preventedbetween the two teatcups of the respective pair.
 2. A method accordingto claim 1, wherein said control comprises that the first phase of oneof the teatcups does not occur at the same time as the third phase ofthe other teatcup.
 3. A method according to claim 1, wherein saidcontrol comprises that said cycle of one of the teatcups is phasedisplaced in relation to said cycle of the other teatcup with a phasedisplacement, which is so controlled that it does not exceed a maximumphase displacement F_(max), wherein F_(max)=(t_(d)/T)*360° ift_(d)<t_(b), and F_(max)=(t_(b)/T)*360° if t_(b)<t_(d).
 4. A methodaccording to claim 3, wherein said control comprises that the phasedisplacement is greater than F_(max)−10°.
 5. A method according to claim1, including the step of operating the pulsator at a pulsationfrequency, wherein the pulsation frequency is controlled to be equalwith or less than 200 cycles per minutes.
 6. A method according to claim5, wherein said control comprises that said cycle of one of the teatcupsis phase displaced in relation to said cycle of the other teatcup by aconstant phase displacement in the interval 80°-100°.
 7. A methodaccording to claim 1, wherein the pulsation frequency is controlled tobe between 300-400 cycles per minute.
 8. A method according to claim 7,wherein said control comprises that said cycle of one of the teatcups isphase displaced in relation to said cycle of the other teatcup by aconstant phase displacement in the interval 35°-55°.
 9. A methodaccording to claim 1, wherein the first pressure level is an atmosphericpressure.
 10. A method according to claim 1, wherein the second pressurelevel is a subpressure of about 50 kPa.
 11. A method according to claim1, wherein a complete milking operation comprises at least an initialmassage period and an main milking period, wherein said control isarranged to be performed during the initial massage period.
 12. A devicefor milking an animal, comprising: a milking machine having at least apair of teatcups each comprising a liner for receiving a teat of theanimal, wherein these liners internally are subjected to a subpressurefor extracting milk from the respective teat; a pulsator which isarranged, via a pulsation chamber of each teatcup, to subject the linerof the teatcup to a cyclically pulsating pressure from the outside,which pressure has a cycle with a time period T, wherein said cyclecomprises, a first opening phase which has a first time period t_(a) andduring which the pressure in the pulsation chamber drops from a firstpressure level to a second pressure level, a second open phase, whichhas a second time period t_(b) and during which the pressure in thepulsation chamber is essentially constant at the second pressure level,a third closing phase, which has a third time period t_(c) and duringwhich the pressure in the pulsation chamber rises from the secondpressure level to the first pressure level, a fourth closed phase, whichhas a fourth time period t_(d) and during which the pressure in thepulsation chamber is essentially constant at the first pressure level;and a control which is arranged, when both the second t_(b) and fourtht_(d) time periods are less than the half time period T for the totalcycle, to control the cyclically pulsating pressures of the respectivepulsation chamber in such a way that a flow of milk between the twoteatcups of the respective pair is prevented.
 13. A device according toclaim 12, wherein said control is arranged to perform said control insuch a way that the first phase of one of the teatcups does not occur atthe same time as the third phase of the other teatcup.
 14. A deviceaccording to claim 13, wherein said control is arranged to perform saidcontrol in such a way that said cycle of one of the teatcups is phasedisplaced in relation to said cycle of the other teatcup by a phasedisplacement which is so controlled that it does not exceed a maximumphase displacement F_(max), wherein F_(max)=(t_(d)/T)*360° ift_(d)<t_(b), and F_(max)=(t_(b)/T)*360° if t_(b)<t_(d).
 15. A deviceaccording to claim 14, wherein said control is arranged to perform saidcontrol in such a way that said phase displacement is greater thanF_(max−)20°.
 16. A device according to claim 12, wherein a milkingoperation comprises at least an initial massage period and a mainmilking period, and wherein said control is arranged to perform saidcontrol during the initial massage period.
 17. A method for milking ananimal comprising the steps of: providing a milking machine whichincludes at least one pair of teatcups, each of said teatcups includinga liner having a milk guiding passage adapted for receiving the teat ofan animal and a pulsation chamber; providing a pulsator connected to thepulsation chamber; subjecting the milk guiding passage within the linerto a vacuum to extract milk from the teats of the animal; operating thepulsator to subject the liner of the teatcup to a cyclically pulsatingpressure from the outside, which pressure has a cycle within a timeperiod T having (a) a first opening phase having a time period t_(a)during which the pressure in the pulsation chamber drops from a firstpressure level to a second pressure level, (b) a second open phasehaving a time period t_(b) during which the pressure in the pulsationchamber is substantially constant at the second pressure level, (c) athird closing phase which has a time period t_(c) during which thepressure in the pulsation chamber rises from the second pressure levelto the first pressure level, and (d) a fourth closed phase which has afourth time period t_(d) and during which the pressure in the pulsationchamber is substantially constant at the first pressure level, andcontrolling the cyclically pulsating pressures of the respectivepulsation chambers of the teatcups to prevent a flow of milk between thetwo teatcups when both the second t_(b) and fourth t_(d) time periodsare less than half of the time period T for the total cycle.
 18. Amethod according to claim 17, wherein said controlling step includespreventing the first phase of one of the teatcups from occurring at thesame time as the third phase of the other of the teatcups.
 19. A methodaccording to claim 17, wherein said controlling step includes displacingthe cycle of one of the teatcups in relation to the cycle of the otherof the teatcups to provide a phase displacement not exceeding a maximumphase displacement F_(max), wherein F_(max)=(t_(d)/T)*360° ift_(d)<t_(b), and F_(max)=(t_(b)/T)*360° if t_(b)<t_(d).
 20. A methodaccording to claim 17, wherein the controlling step includes controllingthe cycles to a frequency of less than or equal to 200 cycles perminute.
 21. A method according to claim 17, wherein the controlling stepincludes controlling the cycles to a frequency of between 200 and 400cycles per minute.
 22. A method according to claim 17, wherein thesecond pressure level is a vacuum of about 50 kPa.
 23. A methodaccording to claim 17 wherein the milking of the animal includes aninitial massage period and a main milking period, and wherein thecontrolling step is performed during the initial massage period.